Aircraft observations of NH3 from agricultural sources

Ammonia (NH₃) is mainly emitted in the atmosphere by anthropogenic activities, especially by agriculture. Excess emissions greatly disturb ecosystems, biodiversity, and air quality. Despite our awareness of these deleterious consequences, NH₃ concentrations are increasing in most industrialized countries. This underlines the need for more stringent regulations and good knowledge of the species gained through effective monitoring.

Since a decade, NH₃ is monitored from space, daily and globally, with thermal infrared sounders. However, their coarse spatial resolution (above 10 km) renders accurate quantification of NH₃ sources particularly challenging. Indeed, only the largest and most isolated NH₃ point sources have been identified and quantified from current observations and often only by exploiting long-term averages. To address the urgent need for better constraining NH₃ emissions, a new satellite, called Nitrosat, has been proposed in response to the 11^th ESA’s Earth Explorer call. The mission aims at mapping simultaneously NO₂ and NH₃ at a spatial resolution of 500 m at a global scale. With the support of ESA, almost 30 aircraft demonstration flights took place in Europe between 2020 and 2022. These flights mapped gapless areas of at least 10 by 20 km containing various sources of NO₂ and NH₃ using two instruments: the SWING instrument targeting NO₂ in the UV-VIS and Hyper-Cam LW measuring infrared spectra to observe NH₃.

Here we present NH₃ observations from campaigns performed in Italy in spring 2022. The Po Valley was the main target, as it is the largest (agricultural) hotspot of NH₃ in Europe.  Despite the presence of large background concentrations in the Po Valley, we show that the infrared measurements are able to expose a multitude of local agricultural hotspots such as cattle farms. A particularly successful campaign covering the region from Vetto to Colorno demonstrates measurement sensitivity to the gradual increase of NH₃ background concentrations outside and inside the Po Valley. We also discuss flights carried out further south in Italy targeting other emissions of NH₃, such as those from a soda ash plant, and the emissions from a fertilizer release experiment that was organized in collaboration with a farmer. We present the measurements both at their native horizontal resolution of 4 m and downsampled at the 500 m resolution of Nitrosat.